Sensory Deficits. Children with autism tend to have extreme reactions to sensory stimulation. Their senses may become hypersensitive (over-sensitive) or hyposensitive (under-sensitive). Hypersensitive children find themselves overloaded with even moderate levels of sensation, and work to block out sensory inputs such as light, sound and touch. Hyposensitive children, on the other hand, are not stimulated enough by normal sensory inputs and typically seek out extra stimulation. To illustrate, children who are hypersensitive to touch sensations may tantrum when they are touched, while hyposensitive children may crave and seek out strong hugs that provide deep pressure. Children with high pain tolerances may injure themselves quite significantly but carry on as though nothing has happened, while oversensitive children may find simple touches or textures to be intolerable.
Children with autism may also display synesthesia, a neurologically-based syndrome where sensations become confused with one another. Sounds may be experienced as touches, for example, or as visual stimulation. For example, children with autism may cover their eyes when they hear a loud sound. Children with autism's sensory synesthesia and sensitivity symptoms occur for neurological reasons. Their brains have difficulty properly filtering sensory inputs. Their brains do not always know what to block out and what to receive, or where sensations are supposed to go.
Fine Motor Deficits. Movement skills are typically divided into two categories: gross motor skills and fine motor skills. Gross motor skills involve large-scale coordinated activities such as walking, while fine motor skills involve detail-oriented activities such as drawing, sewing or playing a musical instrument.
Children with autism frequently show developmental delays in developing fine motor skills. While some children enjoy fine motor activities like lacing their shoes or coloring, others become very agitated when directed to complete fine motor activities. Writing is especially troublesome for some children. Many choose to use a keyboard rather than writing things out by hand.
Part of the issue children with autism have with fine motor activities is that they tend to interfere with their need to engage in stereotyped repetitive movements and self-stimulatory behaviors. Children with autism with hyposensitivities to sensory stimulation constantly feel under-stimulated, and engage in a variety of self-stimulation behaviors such as hand flapping or rocking just to help themselves feel more 'normal'. Likewise, hypersensitive children may engage in self-stimulation as a means of blocking out otherwise overwhelming environmental stimulation. In either case, children with autism find it aversive to be prevented from self-stimulating by the need to concentrate on tasks and are likely to resist efforts to motivate them to complete such tasks.
Self-stimulation behaviors are often varied in nature. In addition to hand flapping and rocking, children with autism may engage in visual self-stimulatory behaviors. They may squint their eyes, or otherwise defocus their eyes to create odd visual sensations. Alternatively, they may engage in "sighting"; repetitiously focusing closely on an object, then pulling away, and then repeating the process over and over.
Gross Motor Deficits. Children with autism commonly have difficulty walking naturally. For instance, they may "toe-walk", stepping only on the front portion of their feet, in place of a normal relaxed walking pattern. This practice may lead to irregular muscle development in the calves.
Many children with autism do not develop a normal sense of themselves in relation to their environments. They lack awareness of where their bodies are in relation to their surroundings. As a result of this lack of environmental awareness, some children become very accident-prone and tend to bump into objects. However, many individuals with autism demonstrate superior gross motor skills and balance, even though they lack body awareness.